The present invention relates to a coating for wood panels to reduce corrosion of metallic members attached thereto.
Oriented strandboard (OSB) panels are commonly used as wall sheathing in the construction of residential homes. These panels are attached directly onto the framing members of a house. Traditionally, the framing members have been wood studs. It is recognized in the construction industry that OSB wall sheathing panels, which are typically {fraction (7/16)}xe2x80x3 thick and 4xe2x80x2xc3x978xe2x80x2 in length can be attached to wood studs by use of nails or screws without concern of any negative interaction between the contacting building materials.
Due to a general decline in the quality of wood studs and erratic prices over the last decade, steel studs have become substantially more common in residential home construction. While steel studs are generally more expensive than wood studs, they have the advantage of being more geometrically perfect, more stable with respect to relative humidity changes, and more consistent from stud to stud. In contrast, builders must sort through shipments of wood studs and separate the straight studs from the warped, bowed and twisted studs.
Steel studs are galvanized in order to make them more corrosion resistant. In the galvanizing process a thin layer of zinc is deposited on the outer surface of the steel studs. This outer layer of zinc is more easily oxidized than the steel. Thus, the zinc layer becomes sacrificial in harsh, oxidative, wet environments where steel is likely to corrode.
As steel studs became more commonly used, it was discovered that they were corroding at an unusually rapid rate when OSB wall sheathing was attached to them. The majority of the corrosion has been found to occur at the sheathing-to-stud contact points. In fact, corroded steel studs often have a visible corrosion pattern that mirrors the pattern of the surface strands in the contacting OSB.
An accelerated corrosion test has been used in North America and Japan to evaluate the rate of corrosion of steel studs that are attached to wood sheathing panels. In this test sections of wood sheathing are tightly screwed to sections of galvanized steel studs and the assemblies are stored in chambers at a temperature of 50xc2x0 C. and a relative humidity of 95% for approximately 800 hours. Plywood sheathing has been associated with minimal corrosion in this test, but significant corrosion has been observed when OSB sheathing has been used. In almost all cases this corrosion is manifest as brown colored, strand-shaped stains that seem to penetrate into the stud surface. A white residue, which is believed to be zinc oxide, is also commonly observed. In the most severe cases red and black deposits, which are believed to be corrosion products of iron, are also present on the stud surface.
The mechanism of the corrosive action is not clearly understood. We have theorized that some unique extractive(s) in the OSB is corroding the steel surface.
We have developed a formulation which can be applied as a coating to the contacting surface of the OSB wall sheathing during the panel manufacturing process. This coating effectively prevents the OSB wall sheathing from corroding steel studs.
In one aspect, the present invention provides an anticorrosion formulation for coating wood based panels to inhibit the corrosion of metallic members in contact with the panel. The formulation is an aqueous formulation that includes boric acid and a group II metal hydroxide selected from beryllium hydroxide, magnesium hydroxide, calcium hydroxide, strontium hydroxide, and barium hydroxide. In one embodiment, the formulation includes a binding agent, preferably carboxylated styrene-butadiene latex.
In another aspect of the invention, a wood based panel coated with the anticorrosion formulation and a method for forming the coated panel is provided.